Tetraquark Masses In A Relativistic Quark Model

Recently, many interesting new meson states were discovered experimentally, some of which do not fit into the quark model easily. So far, one suggests various possible structures such as glueball, tetraquark, molecular, hybrid etc.Since quantum chromodynamics (QCD) is non-perturbative in the infrared region as the basic theory of strong interaction, the potential model as one of various models inspired by QCD has been developed to explain the properties of hadron. In this model, the quark interactions are described by effective potentials.We hope that the mass of tetraquark can be investigated in potential quark model, and some valuable information about the underlying structure of some exotic mesons can be found in our work. Adopting the quark-quark and diquark-antidiquark interactions are the sum of one-gluon exchange with the mixture of scalar and vector linear confining potentials, the masses of tetraquark are calculated within the framework of the relativistic quark model and diquark model. The obtained results support the identification of f₀(600), k(800), f₀(980) and a₀(980) as the light tetraquarks and of D_s(2317), D_s(2457), D_s(2632), X(3872), Y(3940) as the heavy tetraquarks.This thesis is organized as follows: the first section is an introduction. The second section is a short overview of the theoretical and experimental progress in the field of some exotic mesons. In the third section, adopting the assumption that the quark-quark and diquark-antidiquark interactions are the sum of the usual one-gluon exchange and the mixture of linear scalar and vector potentials, we construct the relativistic corrections of order v²/c² to these interactions. Then the Jaffe-Wilczek diquark model is introduced in detail. In the last section, a variational calculation is performed to the masses of heavy and light tetraquarks within the framework of the relativistic quark model and diquark model, eventually, a discussion about which exotic mesons can be identified as tetraquarks is presented.